Seth and his two male cousins are homosexual. the two cousins are on his mother's side of the family, as would be predicted by a genetic explanation for homosexuality, called

That explanation is called the fertile females theory. This theory indicates that women may have a gene, present on the X chromosome that makes them more fertile. When that gene is passed over to a male son it reflects on sexual attraction for the same gender. The case exposed above could be supported by this theory as the cousins of Seth come from his mother side, meaning that they could also have had inherited that gene Seth had also inherited.